N Queen Board Problem in SV Constraint

SystemVerilog
, , ,
2

In reply to qkuang:
A key part of this problem is the diagonals have different lengths. You need to guard

module top;
  parameter N = 8;
  class queen_board;
    rand bit queen_b[N][N];
    constraint c {
      foreach(queen_b[i]) {
        queen_b[i].sum() with (int'(item)) == 1; // row
        queen_b.sum(b) with (int'(queen_b[b.index][i])) == 1; // col
        // descending diagonals
        queen_b.sum(b) with (i+b.index<N? int'(queen_b[b.index][i+b.index]) : 0) <= 1;
        queen_b.sum(b) with (i+b.index<N? int'(queen_b[i+b.index][b.index]) : 0) <= 1;
        // ascending diagonals
        queen_b.sum(b) with (i+b.index<N? int'(queen_b[N-1-i-b.index][N-1-b.index]) : 0) <= 1;
        queen_b.sum(b) with (i+b.index<N? int'(queen_b[N-1-b.index][N-1-i-b.index]) : 0) <= 1;
      }
    }
  endclass
     
  queen_board qb = new;
      initial repeat(5) begin
    assert(qb.randomize());
    foreach(qb.queen_b[i]) $display("%p",qb.queen_b[i]);
    $display;
  end
endmodule